The present invention relates to conductive paste for a via connection employed in production of multilayer ceramic substrates on which LSI, IC or chip components are mounted.
In order to produce multilayer ceramic substrates, the green sheet process and printing process are known and are widely used. The green sheet process has advantages such that a large number of layers can be stacked and fine circuit patterns can be formed but is disadvantageous in that production yield is low and flexibility for changes of circuit patterns is poor. On the other hand, the printing process has merits such that the process is simple, flexibility for changes of circuit patterns is excellent and production yield is high. However, the printing process has drawbacks such that a large number of layers cannot be stacked due to uneven portions formed on the surface of the substrate by the circuit patterns and fine circuit patterns cannot be formed. By incorporating the advantages of these two known processes, a hot stamping process has been proposed in which a hot stamping sheet having a circuit pattern embedded in an insulating layer is stamped and laminated on a ceramic substrate.
Meanwhile, a vital point in technology for producing multilayer ceramic substrates resides in a technique for connecting circuit layers. Generally, in order to connect the circuit layers, holes called "via holes" are formed at predetermined locations on a circuit and conductive material is filled into the via holes. In the green sheet process and hot stamping process, insulating and conductive layers are laminated on one another so as to be formed integrally with each other and then, are fired simultaneously. Therefore, in the known processes, a problem arises such that if firing of the conductive material in the via holes and firing of insulating material bounding peripheries of the via holes are not synchronized with each other accurately, a circuit is disconnected from the via conductor or gaps are produced in the via holes, thereby resulting in extreme deterioration of reliability of a connection.